Kerosene lamps face gravity-powered usurper

A bag of rocks and some height provide the power for GravityLight.

A London design consultancy has developed a cheap, clean, and safer alternative to the kerosene lamp. Kerosene burning lamps are thought to be used by over a billion people in developing nations, often in remote rural parts where electricity is either prohibitively expensive or simply unavailable. Kerosene's potential replacement, GravityLight, is powered by gravity without the need of a battery—it's also seen by its creators as a superior alternative to solar-powered lamps.

Kerosene lamps are problematic in three ways: they release pollutants which can contribute to respiratory disease; they pose a fire risk; and, thanks to the ongoing need to buy kerosene fuel, they are expensive to run. Research out of Brown University from July of last year called kerosene lamps a "significant contributor to respiratory diseases, which kill over 1.5 million people every year" in developing countries. The same paper found that kerosene lamps were responsible for 70 percent of fires (which cause 300,000 deaths every year) and 80 percent of burns. The World Bank has compared the indoor use of a kerosene lamp with smoking two packs of cigarettes per day.

The economics of the kerosene lamps are nearly as problematic, with the fuel costing many rural families a significant proportion of their money. The designers of the GravityLight say 10 to 20 percent of household income is typical, and they describe kerosene as a poverty trap, locking people into a "permanent state of subsistence living." Considering that the median rural price of kerosene in Tanzania, Mali, Ghana, Kenya, and Senegal is $1.30 per liter, and the average rural income in Tanzania is under $9 per month, the designers' figures seem depressingly plausible.

Approached by the charity Solar Aid to design a solar-powered LED alternative, London design consultancy Therefore shifted the emphasis away from solar, which requires expensive batteries that degrade over time. The company's answer is both more simple and more radical: an LED lamp driven by a bag of sand, earth, or stones, pulled toward the Earth by gravity.

It takes only seconds to hoist the bag into place, after which the lamp provides up to half an hour of ambient light, or about 18 minutes of brighter task lighting. Though it isn't clear quite how much light the GravityLight emits, its makers insist it is more than a kerosene lamp. Also unclear are the precise inner workings of the device, though clearly the weighted bag pulls a cord, driving an inner mechanism with a low-powered dynamo, with the aid of some robust plastic gearing. Talking to Ars by telephone, Therefore's Jim Fullalove was loath to divulge details, but did reveal the gearing took the kinetic energy from a weighted bag descending at a rate of a millimeter per second to power a dynamo spinning at 2000rpm.

The company has turned to indiegogo to crowdfund an initial run of 1,000 GravityLights. These will be given to rural villagers in India, and in several African countries for testing, with their feedback informing the design of an improved Mark II version for wider manufacture. Though GravityLights are expected to cost $10, it's hoped that the refined, more efficient Mark II GravityLight will cost $5 or less. Its makers assert that for villages in the developing world, a $10 GravityLight would pay for itself within three months by negating the need to buy kerosene.

Ultimately, GravityLight's creators envision a time when the device could become a low-powered off-grid energy hub for remote homes, powering not only a light (or a string of lights) but perhaps also phones or e-reader Wikipedia clients that connect, with or without cables, to the GravityLight. These are all long-term projects that form the company's deciwatt research initiative, though such projects may be dependent upon cell tower or satellite availability. Their goal for now, though, is to establish the GravityLight itself.

At the time of writing, the funding campaign has received over $380,000—well in excess of the $55,000 goal and enabling the development of accessories. Among the available pledges, $25 will sponsor a GravityLight for shipping to the developing world, while $60 will do the same—and secure a GravityLight of your own.

GravityLight in action.

Ars Science Video >

A celebration of Cassini

A celebration of Cassini

A celebration of Cassini

Nearly 20 years ago, the Cassini-Huygens mission was launched and the spacecraft has spent the last 13 years orbiting Saturn. Cassini burned up in Saturn's atmosphere, and left an amazing legacy.

James Holloway
James is a contributing science writer. He's a graduate of the Open University, with a B.Sc. in Technology and a Diploma in Design and Innovation. Twitter@jamesholloway

Lack of actual lumen specs is disappointing. Seems like this should be easily reverse engineered, and that for crowd sourcing, they would give more details.

I saw this and thought "grandfather clock", so I suppose someone more motivated than me could calculate the potential energy of a bag of rocks and the energy requirements to power a 10-watt LED for 30-minutes.

Lack of actual lumen specs is disappointing. Seems like this should be easily reverse engineered, and that for crowd sourcing, they would give more details.

I saw this and thought "grandfather clock", so I suppose someone more motivated than me could calculate the potential energy of a bag of rocks and the energy requirements to power a 10-watt LED for 30-minutes.

Veering off topic a bit, one of my kids is showing a real interest in science in school so I addition to his normal Christmas loot I bought him a copy of Richard Feynman's 'Six Easy Pieces". This would be a great hands on example of gravitational potential energy in action.

Assuming a 10kg weight falling a meter, this gives us about 98 Joules of energy - which is not a lot.

It's enough to run a 1 watt light for 98 seconds. Assuming a run time of a half an hour, we'd require a 0.03 Watt light. Assuming a highly efficient LED of 90 lumens/Watt, you'd get about 2.5 lumens - which is basically a pretty dim LED flashlight.

I first heard of this idea few weeks ago, and ever since then I keep thinking about how this truly a brilliant idea. I hope they can keep costs low enough to make it feasible for poor families, and that it is rugged to stand up to years of abuse.

I'm no expert, but I can imagine this old-new concept making a significant positive economic impact where it's needed. Also, I would warn against investing in small-time kerosene dealers now.

Assuming a 10kg weight falling a meter, this gives us about 98 Joules of energy - which is not a lot.

It's enough to run a 1 watt light for 98 seconds. Assuming a run time of a half an hour, we'd require a 0.03 Watt light. Assuming a highly efficient LED of 90 lumens/Watt, you'd get about 2.5 lumens - which is basically a pretty dim LED flashlight.

It'd probably be hung higher than a meter, 2 meters might be closer to the height.

The future holds so many exciting possibilities to energy alternatives. This is one of many. I'm so glad to see that people are breaking the thinking pattern that necessitates fossil fuels, batteries, solar panels, or battery/solar panel charging combos.

How about a plastic block-and-tackle that multiplies the amount of rope pulled out of the device for a given amount of vertical drop? With a "double tackle" rig, 4x mechanical advantage (ignoring losses due to friction etc), hanging four times more weight from the pulleys applies roughly the same original force to the free end, pulling rope out of the device at the same rate as before but with the weight dropping 1/4 as fast.

On the other hand that would require 4x more rope, a bigger spool inside the device, the pulleys themselves, knowledge of how to rig a block and tackle ... all to lift a bag of rocks every 2 hours instead of every 30 minutes. Oh well, it was an interesting thought experiment.

Technically, isn't it muscle-powered instead of gravity-powered? I mean, you're using your muscles to hoist the bag into place*, providing it with the potential energy that in turn powers the lamp until the process needs to be repeated.

It's not like the inventor found a way to tap into gravity to make the machine run without any human intervention the way solar-powered systems can do given enough sunlight.

Then again, "gravity-powered" makes for much better PR copy. ;-)

(*:Yes, you could use a machine to do the lifting for you, but that would be both inefficient and not the use case this product was designed for.)

Isn't it more technically muscle powered rather than gravity powered? Or is that just me being nitpicky?

Edit: ^^^ Curse you Baumi!

You could attach the weight to pretty much anything, which would be interesting - like a chair: just sit down and it pulls the cord down over the course of half an hour, at which point you just have to stand up and sit down again. Or park your car on a ramp at night (not that the target market has cars, but how about a cow?) which could provide energy for a stove or something...

How about a plastic block-and-tackle that multiplies the amount of rope pulled out of the device for a given amount of vertical drop? With a "double tackle" rig, 4x mechanical advantage (ignoring losses due to friction etc), hanging four times more weight from the pulleys applies roughly the same original force to the free end, pulling rope out of the device at the same rate as before but with the weight dropping 1/4 as fast.

On the other hand that would require 4x more rope, a bigger spool inside the device, the pulleys themselves, knowledge of how to rig a block and tackle ... all to lift a bag of rocks every 2 hours instead of every 2 minutes. Oh well, it was an interesting thought experiment.

Pulleys would have no effect. Potential energy is simply a function of mass, acceleration due to gravity and distance from ground/bottom of system. You cannot get more energy out of the system than its potential.

This idea surfaced about 3 years ago and at the time there weren't any LEDs sufficiently efficient enough to crank out enough light for enough time to make it worthwhile. LEDs have gotten better in the intervening years but not *that* much better.

The fact that the promoter isn't releasing details makes me wonder if it's just a way to extract money from magic crystal worshipers.

How about a plastic block-and-tackle that multiplies the amount of rope pulled out of the device for a given amount of vertical drop? With a "double tackle" rig, 4x mechanical advantage (ignoring losses due to friction etc), hanging four times more weight from the pulleys applies roughly the same original force to the free end, pulling rope out of the device at the same rate as before but with the weight dropping 1/4 as fast.

On the other hand that would require 4x more rope, a bigger spool inside the device, the pulleys themselves, knowledge of how to rig a block and tackle ... all to lift a bag of rocks every 2 hours instead of every 2 minutes. Oh well, it was an interesting thought experiment.

Pulleys would have no effect. Potential energy is simply a function of mass, acceleration due to gravity and distance from ground/bottom of system. You cannot get more energy out of the system than its potential.

He did in fact mention more mass (4x more weight hanging from the pulley's) and distance (would require 4x more rope).

Assuming a 10kg weight falling a meter, this gives us about 98 Joules of energy - which is not a lot.

It's enough to run a 1 watt light for 98 seconds. Assuming a run time of a half an hour, we'd require a 0.03 Watt light. Assuming a highly efficient LED of 90 lumens/Watt, you'd get about 2.5 lumens - which is basically a pretty dim LED flashlight.

It'd probably be hung higher than a meter, 2 meters might be closer to the height.

Yes, it's really disappointing that Ars would not do the math on this, especially as it's been done by several bloggers. It looks like this is a good looking idea that is unfortunately not going to work. So one has to ask, with that much money involved, if those people are honest.

I mean, what if there's already a source of energy, like some kind of flowing water? If the ballast bag is moving 1mm/sec (as indicated in the article), it might not take too much water to achieve a similar effect. While the mechanism for routing water might be relatively complex, if you could use e.g. a solar basin (a few hours of solar UV kills a lot of nasties) with a small waterwheel, then you'd get some low-effort lighting as well as some clean(er) drinking water.

Assuming a 10kg weight falling a meter, this gives us about 98 Joules of energy - which is not a lot.

It's enough to run a 1 watt light for 98 seconds. Assuming a run time of a half an hour, we'd require a 0.03 Watt light. Assuming a highly efficient LED of 90 lumens/Watt, you'd get about 2.5 lumens - which is basically a pretty dim LED flashlight.

It'd probably be hung higher than a meter, 2 meters might be closer to the height.

Still, even at 5 lumens this is less than a kerosene lamp.

Some of the pictures at the bottom argue for a 2m drop. The other half of the equation is "which kerosene lamp" or more broadly are the lamps they're looking to replace similar to those we might buy; or much dimmer models designed to make the liter of fuel they're buying last a full month. I've never used one so I don't have any idea how fast it burns fuel.

The liter would have ~37 megajoules of energy; but I suspect only a small fraction of that is converted to light when burned.

How about a plastic block-and-tackle that multiplies the amount of rope pulled out of the device for a given amount of vertical drop? With a "double tackle" rig, 4x mechanical advantage (ignoring losses due to friction etc), hanging four times more weight from the pulleys applies roughly the same original force to the free end, pulling rope out of the device at the same rate as before but with the weight dropping 1/4 as fast.

On the other hand that would require 4x more rope, a bigger spool inside the device, the pulleys themselves, knowledge of how to rig a block and tackle ... all to lift a bag of rocks every 2 hours instead of every 2 minutes. Oh well, it was an interesting thought experiment.

Pulleys would have no effect. Potential energy is simply a function of mass, acceleration due to gravity and distance from ground/bottom of system. You cannot get more energy out of the system than its potential.

He did in fact mention more mass (4x more weight hanging from the pulley's) and distance (would require 4x more rope).

The pulleys are irrelevant here: They are just a way to create extra friction, as far as getting energy out of the system is concerned. The mass could make a difference.

The standard usefulness of pulleys is that they allow you to convert high energy*short distance to low energy*long distance, but the total amount of energy transfered is the same. (Not counting friction losses in the pulleys...) Since they already have a mechanism to extract energy at the constant rate they need, all we care about is the total energy.

Yields, if my math is correct, 1.18 Watts as it runs. Output would be 0.2 Watts. Thanks to Slowpoke for catching my mistake.

Sounds tiny (because it is), but from what I've found online this could be as much as 85 lumens from a good quality LED.

Food for thought.

Above link no longer applies, as obviously a 0.2W input is insufficient to achieve full output from a 1W LED. Either that, or we'll have to lift 50kg, or suffer through a 3-minute light source. Neither of which seems palatable.

Why is everyone doing the math with 10 kg weights? Raising a 25 kg weight to eye level is easy for someone who is reasonably healthy, and there is no reason why you couldn't do this multiple times for one charge. After that, it's all about how much weight the pulley system can hold.

Stealing DanNeely's napkin, if you get 50 kg to eye level, or ~1.5m, and the half the use time to 15 minutes, you end up with about 40 lumens over that time. That's definitely enough light for simple tasks.

Why is everyone doing the math with 10 kg weights? Raising a 25 kg weight to eye level is easy for someone who is reasonably healthy, and there is no reason why you couldn't do this multiple times for one charge. After that, it's all about how much weight the pulley system can hold.

Stealing DanNeely's napkin, if you get 50 kg to eye level, or ~1.5m, and the half the use time to 15 minutes, you end up with about 40 lumens over that time. That's definitely enough light for simple tasks.

The indiegogo page mentioned 20 pounds. It's not clear if that was an max weight before breaking, minimum useful weight, the weight used for their 18-30 minute runtime, or something else. Under those circumstances hand waving 20lb to 10kg isn't unreasonable although I would definitely prefer a strap and container that could hold more.

Why is everyone doing the math with 10 kg weights? Raising a 25 kg weight to eye level is easy for someone who is reasonably healthy, and there is no reason why you couldn't do this multiple times for one charge. After that, it's all about how much weight the pulley system can hold.

Stealing DanNeely's napkin, if you get 50 kg to eye level, or ~1.5m, and the half the use time to 15 minutes, you end up with about 40 lumens over that time. That's definitely enough light for simple tasks.

50 kg? Really? That is pretty damn heavy. 25 kg is not light either, and judging by the size of the ballast bag, there is no way to contain 25 kg of earth/sand/rocks in it. Maybe with lead or some other dense material, but silicates are not that dense.

I wonder about the trade-off with solar here. Sure, batteries degrade, but so do plastic gears. They need to make this cheap, but I wonder how long this would last if used for hours every day. Still a neat idea, though.

I think the idea of lifting 20 lbs every 30 minutes for an incredibly weak 0.05W bulb is not very realistic. I don't really see how that helps kids in poor countries study late at night, for example. Scale it up to realistic numbers and the weights start to get really heavy, or the lift frequency goes up huge.

@Aidolon, I think there might be something odd in your math. Using your numbers I get 196 joules, divided over 15 minutes (900 seconds), gives 0.2W.

@Hypopraxia. There are hand-crank LED flashlights that store the energy in a coiled spring, so that the conversion chain remains mechanical -> electrical -> light without a detour into battery chemical energy. Still hard to generate a lot of energy.

It feels like yet another example of two of my major annoyances: (1) design consultancies with limited engineering abilities making misleading claims, and (2) an innovation that is actually enabled by the low power of LED lights, rather than 'gravity' power.

Abstract:Gravity powered electrical energy generators, particularly for producing lighting is disclosed. The apparatus has a support frame (1, 30) in which a series of gears and a gear-driven generator (20) are mounted. The power to drive the most upstream gear (2) is provided by a weight suspended from a point to one side of the axis of rotation of gear (2). The drive gear of the furthest downstream gear has no teeth so that the final contact between the drive gear and the shaft of the generator (20) is frictional. The gear ratio of the final downstream gear is at least 25. When used for lighting, the apparatus may include one or more high brightness LEDs (40) mounted on the housing (30). By suitable choice of gear ratios, the device may produce thirty minutes of illumination while allowing a 10 kilogram weight to fall through a distance of 1.8 metres.

Came here to post that link. It's the blog site from the guy who does/did Dansdata and he's pretty good at spotting scams etc. There was a similar design a few years back for the 'gravia light' which he hought wouldn't work, but he thinks this one might be semi-useful.

edit: jgedeon - not sure if that patent will be granted as the Gravia lamp basically does the same thing, and also applied for a patent. Maybe given the screwed up patent system it'll be granted, though.

How about a plastic block-and-tackle that multiplies the amount of rope pulled out of the device for a given amount of vertical drop? With a "double tackle" rig, 4x mechanical advantage (ignoring losses due to friction etc), hanging four times more weight from the pulleys applies roughly the same original force to the free end, pulling rope out of the device at the same rate as before but with the weight dropping 1/4 as fast.

On the other hand that would require 4x more rope, a bigger spool inside the device, the pulleys themselves, knowledge of how to rig a block and tackle ... all to lift a bag of rocks every 2 hours instead of every 2 minutes. Oh well, it was an interesting thought experiment.

Pulleys would have no effect. Potential energy is simply a function of mass, acceleration due to gravity and distance from ground/bottom of system. You cannot get more energy out of the system than its potential.

He did in fact mention more mass (4x more weight hanging from the pulley's) and distance (would require 4x more rope).

The pulleys are irrelevant here: They are just a way to create extra friction, as far as getting energy out of the system is concerned. The mass could make a difference.

The standard usefulness of pulleys is that they allow you to convert high energy*short distance to low energy*long distance, but the total amount of energy transfered is the same. (Not counting friction losses in the pulleys...) Since they already have a mechanism to extract energy at the constant rate they need, all we care about is the total energy.

You (and a couple others) didn't read the post close enough. The math was all correct. The assumption is that this device can only support a certain amount of weight, but might be more easily adapted with a longer rope. Thus the pulley would facilitate increasing the weight of the energy supplying mass without increasing the weight on the light itself or the height. I'm not sure if it's practical or not but the post was correct.